The GH/IGF-1 Axis in Chronic Heart Failure

The classic model of Chronic Heart Failure (CHF) is rooted in the overexpression of neurohormonal molecules. To complement this paradigm, increasing evidence indicates that a variety of hormones may be down-regulated in CHF patients. The list includes growth hormone (GH) and its tissue effector insulin-like growth factor-1 (IGF-1). The GH/IGF-1 axis regulates cardiac growth, stimulates myocardial contractility, and influences the vascular system. The relationship between the GH/IGF-1 axis and the cardiovascular system has been extensively demonstrated in numerous studies in animals models and confirmed by the cardiac derangements secondary to both GH excess and deficiency in humans. Impaired activity of the GH/IGF-1 axis in CHF has been described by several independent groups and includes a wide array of abnormalities, including low IGF-1 levels, GH deficiency (GHD), and GH resistance that may be related to the severity of heart disease. According to several observations, these derangements are associated with poor clinical status and outcome. Since the first study of GH therapy in CHF in 1996, several placebo-controlled trials have been conducted with conflicting results. These discordant findings are likely explained by the degree of CHF-associated GH/IGF-1 impairment that may impact on individual responsiveness to GH administration. Biological actions of GH and IGF-1, cardiovascular implication of GH deficiency and GH excess, relation between somatotrophic axis and CHF are discussed. Results from trials of GH therapy, emerging therapeutic strategies, safety issues, and lack in evidence are also reported.